This invention relates in general to a continuous catalytic alkylation process utilizing a solid catalyst bed to effect an alkylation reaction, and more specifically, this invention relates to an application of a simulated moving catalyst bed utilizing a zeolitic catalyst to effect an alkylation reaction in one zone of a catalyst bed and a reactivation of the catalyst in another zone. Even more specifically, this invention relates to reactivating in an alkylation process a crystalline aluminosilicate zeolite catalyst composited with a Group VIII metal hydrogenation agent with a reactivation stream including hydrogen.
One of the problems in carrying out a catalytic reaction is that of catalyst deactivation. In essentially all catalytic reactions, over a period of time the catalyst will lose part of its activity. It is common practice to discard or reactivate a catalyst when its activity is sufficiently low to cause inefficiency or unprofitability, at which point, the catalyst is considered "spent". Various schemes are used to reactivate or regenerate a catalyst depending on catalyst characteristics, the process scheme, and economic considerations. Generally, the operation to regenerate a catalyst is considered unprofitable, although at least in certain processes, some, and even a great benefit is directly derived from a catalyst regeneration operation. When an operating plant must be taken out of service for the purpose of conducting a catalyst regeneration, and production time is lost, the economic liability is especially great. Typical examples of processes which require shutdown of normal operations to regenerate catalyst include naphtha reforming to high octane gasoline, hydrocracking, hydrodesulfurization, and di-olefin saturation, to name but a few, and in these processes, it is common for a plant to be shutdown about 2 to 10 percent of a calendar year for the purpose of catalyst regeneration. In other processes, the deactivation rate of the catalyst is so great that reactors may be installed in duplicate to allow normal operation in one, while regeneration or replacement of the catalyst in the standby reactor takes place. An example of such a process is a process for dehydrogenation of paraffins to olefins, but the technique of providing standby reactors or contactors is more common for simple operations like air drying. Another regeneration scheme is the recent development of continuous regeneration of a small portion of a catalyst bed by continuously removing a catalyst portion from the bed, regenerating it in continuous facilities external to the catalyst bed, and continuously returning regenerated catalyst to the catalyst bed. This method of catalyst regeneration has been successfully applied to a reforming process in which naphtha is upgraded to high octane gasoline. Still another regeneration technique is that commonly employed in fluid catalytic cracking units, wherein during normal operation of the process the entire catalyst bed is continuously moving between a reaction zone and a regeneration zone.
Each of the above described regeneration schemes has benefits and liabilities which make the scheme applicable to a given process and not another. The continuous schemes are becoming more desirable as processing severity increases, resulting in more rapid catalyst deactivation. From a historical viewpoint, it is seen that economics favor increasing reaction severity for many catalytic reactions, resulting in higher product yields and higher product quality, and a greater catalyst deactivation rate. While catalyst development has resulted in more active, more stable catalysts, an emphasis is being placed on maintaining essentially fresh catalyst activity throughout the duration of a catalyst run. In many processes, the increased value of a higher product yield or higher product quality throughout a catalyst run is greater than the increased cost of maintaining a higher catalyst activity, either through more expensive, more stable catalysts or through continuous regeneration schemes.
In the field of alkylation, essentially all existing plant capacity utilizes either hydrofluoric or sulfuric acid fluid catalysts. While it is an objective to develop a catalyst which will yield a higher quality alkylate product and a more economical process, it is also desirable to develop a catalyst which is safer to handle, less corrosive, and less objectionable from an environmental viewpoint than the present acid catalysts. Recent development work has led to several patents related to the use of aluminosilicate zeolite catalysts in alkylation processes, including U.S. Pat. Nos. 3,840,613, 3,549,557, 3,795,714, 3,417,148, 3,251,902, 3,851,004 and others. However, catalysts of the zeolite type suffer from losses of both activity and selectivity over a short period of operation in an alkylation process and require reactivation to maintain a suitable level of activity and selectivity. It has been generally concluded that rapid loss of activity has been the result of adsorption on the catalyst surface of polymeric and polyalkylated hydrocarbons. In U.S. Pat. No. 3,549,557, for example, it is shown that a zeolitic catalyst after about 10 hours or operation loses a substantial portion of its original selectivity and activity, but with periodic reactivation, the catalyst returns to almost original catalytic activity and selectivity. The reactivation procedure used in U.S. Pat. No. 3,549,557 is to stop normal operation of the alkylation process (which includes alkylation of isobutane and butylene at 195.degree. F. and 500 psig.) by stopping olefin flow while continuing isobutane flow, raising the catalyst temperature to 600.degree. F., at which temperature the catalyst is reactivated, lowering the catalyst temperature to alkylation conditions and reintroducing olefin feedstock. In U.S. Pat. No. 3,851,004, a zeolitic catalyst containing a hydrogenation agent of a Group VIII metal is used in an alkylation process, and a reactivation stream including hydrogen is incorporated to periodically reactivate the catalyst. Like the reactivation procedure shown in U.S. Pat. No. 3,549,557, the reactivation procedure of U.S. Pat. No. 3,851,004 is a cyclic one, in which reactants and reactivation media are alternately charged to a catalyst bed, thus requiring periodic and frequent stoppage of normal operation of the catalyst bed in its alkylation function.